Network survivability is of utmost importance in a telecommunications network, since loss of services in the network for only a very short period of time can tremendously affect the operability of the network and cause a significant loss of revenue. The self healing network (SHN) distributed restoration algorithm (DRA) disclosed in U.S. Pat. No. 4,956,835 teaches selecting a K-shortest path for restoring disrupted traffic between adjacent nodes. The '835 method, however, is based on a non-deterministic approach that is subject to the various dynamic delay characteristics present in the network at the particular moment of time that an outage occurs. As a consequence, the '835 method does not guarantee that an optimal restoration path, or alternate route, will be chosen for a given malfunction in the network.
To elaborate, the '835 method theoretically restores traffic in a mesh network by working in parallel in a distributed fashion to select from among the available spare capacity the restoration connections or spare links. Although in theory the '835 distributed method will always select the K-shortest path for restoring the affected traffic, in actuality, this method is affected by the delays encountered by the restoration signatures flooded across all the nodes of the network. This is primarily due to the non-uniform nodal processing delays of the various nodes of the network. In other words, the propagation (or transmission and retransmission) of the restoration signatures (or messages) for both flooding and reverse linking sequences over different alternate routes are limited by the speed in which the various nodes along the various alternate routes detect and process the messages. Putting it differently, the spare capacity provided to a network is based on the assumption that restoration of disrupted traffic will behave according to a shortest path rule. If this shortest path rule is not followed, then restoration may not be possible due to a lack of spare capacity for certain portions of the network. The assumption therefore is that all equipment of the network behave the same uniformly throughout the network. Yet the fact that some devices may take longer than others to process the messages traversing therethrough means that the theoretically shortest path rule, as espoused in the '835 patent, will not always produce a truly optimal restoration route to restore disrupted traffic.